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Simulating Manufacturing Processes

By Patrick WaurzyniakSenior Editor

With today’s complex multitasking machine tools, simulations of manufacturing processes are becoming much more pervasive, both in metalcutting operations simulated with the latest NC simulation and verification packages and at a more macro level through highly realistic 3-D plant-floor visualization systems.

The latest simulation software tools offer much more automation of tasks, easing the demands of programming the complex multitasking/multifunction machines that have become more popular as those systems’ prices have fallen. In addition, developers of enterprise-wide PLM systems have beefed up the collaborative capabilities of their simulation systems, enabling engineers to stretch the global reach of 3-D simulations in assembly planning and validation, 3-D mockup, virtual commissioning, and other advanced simulation functions.

Verifying NC Simulations

Getting precise simulations of NC metalcutting operations are a must with many aerospace/defense applications where a mistake can cost manufacturers dearly when cutting expensive titanium or other exotic alloys. Likewise, many of the components in medical manufacturing operations consist of the most expensive metals, including titanium and cobalt chrome molybdenum, necessitating simulating, verifying, and optimizing NC cutting operations often performed on the most complex new mill-turn and multiaxis/five-axis machining centers.

"The general trend in industry is more automation of more tasks, which in turn creates more complex automation processes," notes Bill Hasenjaeger, product manager, CGTech Corp. (Irvine, CA), developer of the Vericut NC simulation, verification and optimization software. "This consequently requires us to enhance Vericut to simulate these more complex processes. Multifunction machines, such as complex mill-turns, are a good example of this increasing process complexity. Throw in automated part transfer and workholding, flash tools, head-changers, facing heads, and you start to see the complexity of modern CNC machining."

Multifunction machine tools perform both milling and turning operations, he notes, allowing the tool to either spin in milling or instead the tool can be stationary and index each insert into position, acting as a turning tool. "We have to support that. With machine tool headchangers, you’ve got a machine that actually changes the head. On a robot, it would be called changing the end-effector, but on a CNC machine it would be changing the head that holds the cutting tool," Hasenjaeger says. "Or you’ve got a milling machine that can mount a facing head on it automatically and it turns the machine from a milling operation into turning operations. So you start ganging all these things on one machine, it becomes a pretty complex multi-step process that the NC program’s controlling, and we increasingly have to simulate that complicated process."

"If the risk of failure is high, the cost

of failure is high, and simulationis increasingly more critical."

Simulations often are complicated not only by the part shape but also the multiple processes required to product a part, he adds. "The fundamental part shape can be relatively simple, but the processes to produce it can be quite complicated. How critical the process is, is somewhat related to either the schedule on the part, the cost of the materials, or the cost of the in-process part," Hasenjaeger points out. "It’s also the risk of failure. If the risk of failure is high, the cost of failure is high, and then simulation is increasingly more critical."

Simulating G-Code Is Crucial

Being capable of simulating the actual G-code of machine tools is essential to success in metalcutting simulations, according to many observers. The most advanced NC simulation software packages offer simulation of machine-tool G and M-codes instead of just checking CAD/CAM output.

"When simulating the actual NC code, it is necessary to emulate the CNC and how the CNC is connected to the machine tool," says Hasenjaeger. "This emulation feature, which in Vericut is called Vericut Machine Configuration [VMC], is critical to the entire simulation. The emulation must be extremely flexible to be able to configure it to match the CNC machine’s exact behavior. This is very important because modern CNC controls are customized by each machine builder. A Siemens 840D control connected to a DST five-axis machine can look and behave differently than the same CNC connected to a Matsuura five-axis machine."

Simulating from something other than the actual CNC program that will go to the workshop, say APT CL or some internal intermediate toolpath format, is simply not enough, Hasenjaeger adds, as too many things change when a CAM system’s internal path is postprocessed to create the NC program.

With the latest Vericut version 7.2, users also can integrate the package directly into the manufacturing process. A recent new feature, NC Program Review, allows users to review previously processed and saved simulations, step forward and backwards in the NC program at a highly detailed level, and determine the exact cause of NC program problems.

"Many people don’t realize Vericut contains automation tools that allow our customers to automate its simulation and build it into their manufacturing engineering systems," Hasenjaeger explains. "Some of our end users run Vericut as a ‘black-box’ inspection tool—they don’t use it interactively, but instead automatically submit NC programs to Vericut, and then view the simulation results as a kind of ‘go/no-go’ test." If an error is detected, the operator can then use Vericut interactively, he adds, to evaluate the problem and apply corrective measures as needed.

More NC Software Alternatives

A newcomer to the US market, French software developer Spring Technologies Inc. (Cambridge, MA, and Paris) started offering its suite of simulation software recently to customers in North America. The 28-year-old company’s NCSIMUL Solutions suite of tools consists of NCSIMUL simulation, a complete G-code verification solution that offers toolpath preview with precise cycle time calculation; the Optitool utility for optimizing cutting conditions; and NCDOC, a module to standardize shop-floor documentation.

With its NCSIMUL suite, Spring Technologies has a large installed base in Europe with deployments at manufacturers including aerospace giant Airbus, Safran, Eurocopter, and automotive transmission builder ZF Group. The company established resellers in Canada in 2005 and in 2008 in the US before formally creating its US subsidiary in Cambridge in 2010, notes Silvere Proisy, Spring Technologies Inc. general manager. The developer last year tripled its number of US customers, Proisy says.

"A couple of important components of the product that jump out are the type of graphics that we display—we really dig into the detail to see specifically what your machine is doing," notes Brian Basiliere, Spring Technologies account manager, in describing NCSIMUL Version 8.9. "The second that would be paramount is our Toolpath Preview, which is based on the kinematics of the machine tool and can show the actual acceleration and deceleration of the machine. It’s literally a virtual representation of the machine tool."

In addition, Spring is launching a new tool-referencing feature, extending the solution to a 3-D cutting tool library for the CAM simulation linked to real tools and accessories management in the workshop, Proisy adds.

For less complicated two to four-axis parts, simulation is not as critical as it is with more complex parts on five-axis or mill-turn machines, Basiliere notes. "If you do two or three-axis machining, the CAM system’s simulation may be enough even though the toolpath has to go through the postprocessor." With four-axis contouring, simulation becomes critical, Proisy adds of machining mission-critical parts like aerospace impellers or fuel rods for nuclear plants.

"With many parts that cost a lot of money to produce, such as a piece of titanium, making a mistake will cost far more than our software," Basiliere states. "If you have a simulation tool, you can machine the part accurately the first time."

The medical device industry also has shown a lot of interest in simulation systems for parts such as bone screws, he adds, where the size and tolerances have to be exacting. Manufacturers cutting parts for the micromachining and nanomachining markets are turning to simulation packages to ensure getting quality results the first time, adding that "simulation at that level is no problem for our software."

Ease of use is another key area, states Proisy, noting that training for NCSIMUL requires only two days for new users. "One thing where we address that is machine tool builders’ macros, and second is the ease of use, a single process," Proisy says. "We have a limited number of icons, every icon with a specific purpose."

The development agreement between Methods and CAMplete evolved over the last few years after Methods had used CAMplete’s TruePath CAM software on its machines, recalls Rich Parenteau, Methods Machine Tools director of application engineering. "They started in the five-axis field, with flow checking for the stock car and Formula One racers, trying to do a flow check on a motor, then machining that exact flow check to get the desired result, which is very difficult with five-axis," Parenteau says.

"When you’re dealing with multitasking, whether it’s two, three or four turrets or B-axis, the multitasking scenario of turn-mill gives you at least two things going on at once," Parenteau says. "You have to determine, from a safety perspective, what you can do and when something has to wait—that’s why they call it a wait code—something has to wait for something to be completed before you can continue. The wait codes in the programming of the machines are duplicated in the software so you can see that happening and determine that time phase much more accurately to take advantage of reducing that wait time to a minimum."

The CAMplete Turn/Mill package simulates the exact G-code off the postprocessor as Nakamura designed the machine to do, Parenteau notes. "We also have the exact acc and dec [acceleration/deceleration] of the axes in the software, so when you check it in the machine, you will get consistent results at 25% or 100%," Parenteau observes. "And that’s crucial—in many software programs that don’t have that acc and dec, you check it at 25% and it looks good. You go to 100% and you have a crash, because you’re not accurate enough to simulate when it’s at full acc and dec, and there’s a slight difference in those positionings in full acc and dec speed."

The software also takes advantage of Nakamura multitasking machines to give the highest accuracy possible, he notes. Another major advantage is reduced setup times, he states, with CAMplete allowing machinists to do full setups off-line while the machine is cutting.

Improved Simulation Drivers

A provider of both NC-level simulation software and enterprise-wide PLM systems, Siemens PLM Software (Plano, TX) continually works to develop more synergy between its plant simulation and robotics visualizations, as well as enhance the NC simulation within its NX CAM software.

In its latest NX 8 CAM software, users can take advantage of enhanced levels of NC simulation and verification, notes Siemens PLM Software’s Vynce Paradise. "We’re always trying to produce better simulation drivers of G and M codes, with simulation of things like tool changes," Paradise says. "There is more programming in a 3-D model environment and we encourage users to bring in a 3-D machine tool model, where they’re actually programming in the context of the machine."

Simulations in NX also allow viewing dynamic tool motion on the screen, where the programmer can grab a dynamic model of the machine tool and the head will articulate and move along with the key elements of the machine assembly, he notes. "That can be very interesting for programmers to see dynamically. We’re also obviously looking for collisions, against the part and against the machine, and the program will indicate that within certain limits—it’ll show you that machine limits are being exceeded, or that you can’t get a tool to that position."

The Siemens software simulates off the G-code, he adds. "The accuracy depends on how good the driver software is. What the driver software is doing is taking the G-code and it’s emulating, pretending to be the controller software. The analogy that I use here is that it’s like a flight simulator," Paradise states. "The driver software is critical on how well you interpret and simulate the G and M code. That’s all part of the driver system software. The ultimate of this is to take the software that’s used within the real machine controller, as we do with the Siemens Virtual Numerical Control Kernel [VNCK]. We can embed that in NX CAM—it’s the same as the core software on the Siemens Sinumerik machine controllers—and you’ve got a very complete simulation set."

Collaboration Fuels Enterprise-Wide Simulations

With the latest enterprise PLM systems, engineers can much more easily collaborate, breaking down some of the traditional barriers between the design side and manufacturing engineering, notes Tom Hoffman, director of manufacturing engineering solutions, Siemens PLM Software. PLM has provided the mechanism for simulation software to evolve over recent years and cross previous barriers in manufacturing operations, from part manufacturing to assembly manufacturing, while ensuring that quality remains high across both domains, he says. Today’s systems like Siemens’ Teamcenter manufacturing process management coupled with the Tecnomatix suite of digital manufacturing and simulation applications and NX CAM software share data and promote collaboration from the start of a project.

"It allows for much more broader collaboration across the enterprise," Hoffman says. "The silos of information are being exposed and shared more than in the past." With systems like Tecnomatix 10, the simulation/digital manufacturing suite, the discrete plant model is being extended outside of the typical plant throughput analysis, he notes. "You can simulate anything—baggage handling, shipyards."

Lean efforts with value-stream mapping and line balancing can take advantage of increased collaborative capabilities of today’s systems, he notes. "They’re making this connection that brings the top floor of the central engineering function and the shop floor together. In the old days, engineering teams spent countless hours performing field checks working with plant engineers on the site. Today these changes can be documented with local staff and accessed at central engineering, providing access to these changes immediately and expediting the engineering decision process."

Additional capabilities include leveraging simulations in work instruction packages, using the PLM environment to perform dynamic document updates and enabling advanced viewing of 3-D within the documentation instead of static information.

"Simulation is the driver behind a lot of this," Hoffman states. "Over the years, we’ve kept adding tools to it—different anthropomorphic models and human analytics, and more capabilities in the robotic simulation environment. We’re driving simulation in an event-based way that allows engineers the ability to perform logic-driven simulation incorporating devices such as a PLC. This integrated environment, a combination of hardware and virtual, drives the simulation through either the hardware or the virtual to validate the actual code used in the production. You can check and verify the programming, so the old days where you’d do your work in simulation and throw it over the wall to implementation teams is less of a problem and allows them to perform simple floor changes if necessary." ME

This article was first published in the April 2012 edition of Manufacturing Engineering magazine. Click here for PDF.